Of all the questions that might be asked about political life, it would be difficult to find one of greater interest than the ancient query: who rules over whom? It appeals powerfully to our curiosity. We want to know who "runs" things--who makes policy decisions in New York, Washington, London, or the town in which we live. Is it a single powerful individual, an economic elite, a series of elites, the citizens, political bosses, or some variant of...